1. Field of the Invention
The present invention relates to a keypad unit with a key top portion for use in cellular phones, mobile communication devices, remote controls for various household electrical appliances, card remote controls and various keyboards, and also relates to a method of separating a key top portion and a keypad portion from a keypad unit having the key top portion (hereinafter “a keypad with a key top”).
2. Description of the Related Art
In recent several years, the demand of terminals such as cellular phones has expanded rapidly, and design variations of push button switches have increased with the expansion. As described in the publication of Japanese Patent No. 2,627,692, a key top and a keypad are separately molded as a separate member, and a keypad with a key top for a push button switch that is formed by making these stick together with an adhesive is becoming the mainstream because of its excellence in both function and design. Silicone rubber is mainly used for the keypad with the key top because silicone rubber is excellent in cold resistance, heat resistance, weather resistance, precision moldability and electric insulation.
However, silicone rubber is a crosslinked polymer, so the recycling of silicone rubber is not easy. The difficulty in recycling has recently become a big issue as understanding of the global environment is more and more significant.
On the other hand, the use of a thermoplastic elastomer as a material for a keypad instead of silicone rubber is extremely effective in recycling. However, because such a keypad is made of a thermoplastic elastomer, and coupled with a key top that is separately molded, deterioration of the quality of a recycled product results from a recycling process. Thus it is required to separate and classify these.
From such points of view, a keypad with a key top that can be easily recycled has been in demand. Also, there is a demand for a method of easily separating a key top and a keypad.